Numerous types of automotive anti-theft devices are presently manufactured. These devices generally operate in one of two ways.
The first group of devices prevent the operation of an automobile by an unauthorized person through interference in the ignition circuit. Unless these devices are properly disengaged before attempting to start the automobile, the device will prevent the ignition coil of the automobile from being energized and thus prevent the car from operating. This first group of anti-theft devices has a major drawback. If failure occurs in one of the system components while the automobile is in operation, coil current may be interrupted. This results in an immediate loss of power, and in cars equipped with power-steering and power-brakes, an immediate and abrupt change in the control functions of the automobile. This can and has resulted in dangerous situations especially on high speed highways.
The second group of anti-theft devices or systems relies upon an alarm which will sound upon on unauthorized entry or an unauthorized attempt to start the vehicle. These systems rely on trigger systems at key points in the automobile such as passenger compartment doors, hood latches, trunk lids or the like. These systems require numerous auxilliary switches which are often installed by inexperienced people and often placed in paths of water drainage. Failure can sometimes occur at these switch points, completely disabling the system.
Some systems combine elements from both groups to arrive at a more comprehensive anti-theft system. Most of these systems while incorporating the advantages of both systems, also incorporate their problems.